If chilly temperatures, grey skies and drizzle – and in some cases even snow – wasn't already enough to make for a miserable bank holiday weekend, pity those who braved the weather to go to the Legoland theme park in Windsor, Berkshire, to find it closed due to a mystery power cut.

Shortly before the Sunday 10am opening time for the park, the UK's third most popular paid-for tourist attraction, bringing in 1.3m visitors a year, an official message was posted on the Legoland Windsor Facebook site saying a power failure, the cause of which was unknown, had forced its closure.

An update just over an hour later said the park remained closed and that those with pre-booked tickets could use them instead at Chessington World of Adventures, another amusement park about 30 miles away.

The Legoland Facebook page was soon awash with comments from disappointed potential customers. One, Andrea McCormella, wrote: "I know the power cut isn't their fault but surely they should have sent officials out telling us what was going on instead of sitting in traffic for over an hour like we've just done! Now we've got a nice 300-mile drive back home and wasted expenses on a hotel!"

It caps a somewhat miserable experience all round for both visitors and businesses during what is traditionally a busy curtain-raiser to the summer tourist season. Following what was officially the wettest April in a century of weather records, forecasters have warned that the bulk of the UK will experience below-average temperatures and grey skies for most of the weekend.

Saturday was particularly chilly, beginning with low overnight temperatures that dropped to -6C in south-west Scotland. The Grampians and north-west Highlands even saw some brief snow flurries. On Sundayacross the UK, peak daytime temperatures ranged from a tepid 11C to a chilly 5C. Monday is forecast to be a degree or two warmer as a bank of heavy rain sweeps in from the west.

Despite the fresh downpours the Environment Agency's list of flood risks is heavily reduced from last week, with just two warnings – both along the river Nene near Peterborough – and five lower-level flood alerts.

One silver lining has been a general lack of traffic queues, with the exception of those unfortunate to be stuck near Legoland. It would be, the AA predicted, "more of a DIY weekend than a travelling to the seaside one".